I am trying to do the same as the original poster (move the menu to below the header).

I have inserted the above code into my child style.css (correcting for the misspelling of position), however when I adjust the 'top' value the menu bar moves down about 1cm on the screen but no further (regardless of what px value I insert).

Thanks for the reply designbyjesseR. However I get no luck when adding the above code to my child theme. The menu bar doesn't move at all. The only other thing I can think of that might be affecting it is my header. To widen my header I have added the following to my child theme.

Is anybody still having an issue with this? I used the code AJD supplied, with an adjustment to top:500px;
The location of the menu is perfect upon initial fixed sight. However, it hovers as I scroll down the page, in the middle of the page, blocking all text/pictures/etc.
How do I keep the menu fixed - starting below the header (which I have completed) - and then fixed at the top of the page as the reader scrolls to the bottom? Any help is appreciated